This is a competitive renewal application to continue a blind, controlled, direct interview family study of obsessive compulsive disorder (OCD). The overall objective is to use the family study method to investigate the heritability of OCD, its relationship to other anxiety disorders, and possible etiologic heterogeneity. Finding during the first funding period indicate moderate, specific familial transmission of OCD, distinct from other anxiety disorders. However, despite several promising leads, the sample size is too small to effectively investigate either the possible heterogeneity of OCD with respect to familial transmission or its obsessive compulsive personality disorder (OCP). The main objectives during the proposed funding period are to: 1) further evaluate our initial finding of specific familial aggregation by attempting replication in a newly collected independent sample of OCD and control families; and, 2) achieve sufficient sample size to effectively investigate the possible heterogeneity of OCD and its relationship to OC and OCP by combining OCD families from the current and proposed studies. In addition, to begin to investigate possible modes of intergenerational transmission of OCD, segregation analyses will be carried out to test the fit of our data with several models of transmission (e.g., multifactorial, two locus, regressive). The long term objectives of this study are to increase the understanding of the etiology of OCD and its relationship to other anxiety disorders. Improved understanding will enable development of more specific and effective treatment interventions.